1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive membrane element including a piezoelectric/electrostrictive portion having excellent piezoelectric/electrostrictive characteristics, and having a large flexural displacement.
2. Description of the Related Art
Heretofore, a piezoelectric/electrostrictive element has been known as an element capable of controlling micro displacement of the order of sub-microns. In particular, a piezoelectric/electrostrictive element is suitable for the control of the micro displacement. In the element, a piezoelectric/electrostrictive body (piezoelectric/electrostrictive portion) constituted of a piezoelectric/electrostrictive ceramic composition and an electrode portion to which a voltage is applied are laminated on a substrate constituted of a ceramic material. In addition, the element has excellent characteristics such as a high electromechanical conversion efficiency, a high-speed response, a high durability and a saved power consumption. The piezoelectric/electrostrictive element is used in various applications such as a piezoelectric pressure sensor, a probe moving mechanism of a scanning type tunnel microscope, a rectilinear guide mechanism in an ultra-precise working device, a servo valve for hydraulic control, a head of a VTR device, a pixel constituting a flat panel type image display device and a head of an ink jet printer.
Moreover, the piezoelectric/electrostrictive ceramic composition constituting the piezoelectric/electrostrictive body is also variously investigated. For example, there has been disclosed a Pb(Mg1/3Nb2/3)O3—PbZrO3—PbTiO3 three-component solid solution composition, or a piezoelectric/electrostrictive ceramic composition in which a part of Pb in the composition is replaced with Sr, La or the like (see, e.g., Patent Documents 1 and 2). As to the piezoelectric/electrostrictive body itself which is the most important portion for determining piezoelectric/electrostrictive characteristics of the piezoelectric/electrostrictive element, the piezoelectric/electrostrictive element is expected to be obtained which has excellent piezoelectric/electrostrictive characteristics (e.g., piezoelectric d constant).
On the other hand, it is disclosed that when the piezoelectric/electrostrictive body is formed using a piezoelectric/electrostrictive ceramic composition containing as a main component a predetermined PMN-PZ-PT three-component solid solution composition containing Ni or an oxide of Ni, it is possible to manufacture a piezoelectric/electrostrictive element which has excellent piezoelectric/electrostrictive characteristics and in which linearity of a flexural displacement with respect to an electric field is high up to a high electric field region (see, e.g., Patent Documents 3, 4).
However, in view of rapid technical progress in recent years, there is supposed a case where it cannot be said that the piezoelectric/electrostrictive body and the piezoelectric/electrostrictive element disclosed in Patent Documents 3, 4 sufficiently satisfy the piezoelectric/electrostrictive characteristics. Therefore, a demand for the development of the piezoelectric/electrostrictive body or the piezoelectric/electrostrictive element having further improved piezoelectric/electrostrictive characteristics has risen.
FIG. 2 is a sectional view schematically showing one example of a state of crystal particles of the piezoelectric/electrostrictive body constituting the piezoelectric/electrostrictive portion of the conventional piezoelectric/electrostrictive membrane element. As shown in FIG. 2, in the conventional piezoelectric/electrostrictive body, a large number of crystal particles 11, 22 are usually constituted of a plurality of domains 11a to 11c, 12a to 12c having inherent crystal directions 9. Moreover, the adjacent crystal particles 11, 22 are arranged so as to come in contact with each other, and a crystal grain boundary 17 is formed. When an electric field is applied to such a piezoelectric/electrostrictive body, an electrically induced strain is generated by the non-180° rotation of the domains 11a to 11c, 12a to 12c. 
[Patent Document 1] JP-B-44-17103
[Patent Document 2] JP-B-45-8145
[Patent Document 3] JP-A-2002-217464
[Patent Document 4] JP-A-2002-217465
The piezoelectric/electrostrictive body is usually constituted by sintering a large number of crystal particles or the like. Therefore, as shown in FIG. 2, the domains 11a to 11c, 12a to 12c bind one another owing to a crystal direction difference between the adjacent crystal particles 11 and 22 based on a difference between the crystal directions 9 of the domains 11a to 11c, 12a to 12c, and hence it is supposed that the adjacent crystal particles 11, 12 mutually disturb deformation. In consequence, it is supposed that displacement which should originally occur if there were not any influence of the adjacent crystal particles is offset not a little.